Methods and devices for generating decorations or decorative features by printing on an outer surface of a container are known. It is also known to apply multicolored prints to a container by contact-free printing, for example, by inkjet printing, with each print head having a plurality of jets for the application of the different colors of ink. The jets are controlled electrically and individually.
Although the direct printing of containers offers considerable advantages, inter alia in terms of flexibility of the printed image and its design and/or alteration and also with regard to costs, the problem persists that when recycling containers of this kind, container material and printing ink both make their way into the recycling material. This leads to an unwanted contamination of the recycled material.
To resolve this problem, WO 2010/048119 suggests that an additional intermediate or base coat be applied on the outer surface of the particular container. Then, in one or more further processing steps, a multi-colored print is applied to the base coat. A known method for applying the material forming the base coat is spraying. However, spraying is time-consuming for large-area printing. In addition, some of the sprayed or squirted base coat material inevitably escapes into the environment.
The particular decoration thus comprises, in the end, the base coat and the print. With the base coat, not only is an improvement of the adhesion of the print achieved, but there is then also the possibility of selecting the material for the base coat and the printing colors or printing inks taking account of the material of the container so that the adhesion between the print and the base coat is greater than the corresponding adhesion between the base coat and the container.
The adhesion between the base coat and the container is selected so that during the entire container cycle and also in the event of any re-use of the containers, the base coat, with the print imprinted thereon, does not detach from the particular container. But in the event of recycling, the base coat together with the print that still adheres to it, can be detached from the containers or from their walls. The process of detaching the base coat from the container can be carried out, for example mechanically and/or with a suitable liquid medium etc. Examples of materials suitable as a base coat material include polyolefins or other monomers, and plastics or polymers that can be cross-linked by processing with UV radiation.
A difficulty that arises with known solutions is that the fluids used for base coats, coatings, finishing etc. tend to have low viscosity. As a result, it has not been possible to handle them at high machine speeds because of the risk of misting and detachment.